Sweetening of petroleum fractions, such as naphtha boiling range hydrocarbons or other liquid hydrocarbons, which contain mercaptans, also known as sour petroleum fractions, are well-developed commercial processes commonly used in many petroleum refineries. In the sweetening process, mercaptans contained in the feed hydrocarbon stream, sour hydrocarbon stream, are catalytically oxidized to disulfide compounds that remain in the hydrocarbon stream, sweetened hydrocarbon stream. Sweetening processes, therefore, typically do not remove sulfur from the hydrocarbon stream but rather convert the sulfur to an acceptable, non-odorous form. The sweetening process involves admixing an oxygen-containing stream to the sour hydrocarbon stream to supply the required oxygen. The admixture of hydrocarbons and oxygen contacts an oxidation catalyst in an aqueous alkaline environment to oxidize the mercaptans in a mercaptan oxidation unit.
In a typical configuration for the sweetening of full range naphtha from a fluid catalytic cracking (FCC) unit, the mercaptan oxidation unit is located upstream of a naphtha splitter column for conversion of mercaptants to disulfides, so that the disulfides are hydrotreated in a downstream process. However, the current approach requires the temperature of incoming naphtha feed from the FCC unit to the mercaptan oxidation unit to be reduced to achieve appropriate reaction conditions in the mercaptan oxidation unit. The treated effluent from the mercaptan oxidation reactor is again required to be heated before being fed to the naphtha splitter column and hence resulting in inefficient heat management.
Further, in a conventional flow scheme, air is injected at the inlet of the mercaptan oxidation unit for oxidation of mercaptans to disulfides. The amount of injected air is almost 200% higher than the theoretically stoichiometrically required amount, and remains dissolved in the effluent from the mercaptan oxidation unit. Removal of dissolved oxygen is very important for protection of equipment against corrosion and fouling. The design of the naphtha splitter becomes complicated and results in an increase in capital expense because the oxygen has to be purged from the system.
Accordingly, it is desirable to provide processes and apparatuses for the oxidation of mercaptans contained in a feed stream that includes liquid hydrocarbons such as naphtha boiling range hydrocarbons or the like for forming a sweetened hydrocarbon stream with efficient heat management. Additionally, it is desirable to provide processes and apparatuses for the oxidation of mercaptans having a simpler naphtha splitter design at a lower capital expense. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying FIGURE and this background.